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HP-21 repair
10-15-2021, 07:17 PM
Post: #1
HP-21 repair
I have a HP-21 that turns on but only displays a zero on the right of the display, an occasionally 3 zeros across the display. The keyboard is unresponsive. Is that a clear sign the ACT chip is dead or could the problem be caused by something else, such as cross talk between PCB traces, or a defective discrete?
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10-15-2021, 09:30 PM
Post: #2
RE: HP-21 repair
(10-15-2021 07:17 PM)Benoit Maag Wrote:  I have a HP-21 that turns on but only displays a zero on the right of the display, an occasionally 3 zeros across the display. The keyboard is unresponsive. Is that a clear sign the ACT chip is dead or could the problem be caused by something else, such as cross talk between PCB traces, or a defective discrete?

I am not a PANAMATIK, but I'd say it's 95%+ an ACT issue. Smile

--Bob Prosperi
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10-15-2021, 10:56 PM
Post: #3
RE: HP-21 repair
I managed to get a cheap HP-25 awhile back which was advertised as not working. When it arrived, I connected some batteries and it was dead. I opened it up and found moisture on the circuit board. After cleaning it up and drying it out, it sprang into life.

It does prove that simple things like that can make the calculator seem faulty, so a good inspection might help get it going.

Other than that, as Bob pointed out, maybe the Arduous Calculator Thingy has failed.

cheers

Tony
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10-16-2021, 12:46 AM
Post: #4
RE: HP-21 repair
Bob, Tony,
Thank you for your guidance.
I did clean up the inside well and checked that the traces conduct, so I think I am good there.
I will check with Bernhard and make it a 34C.
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10-16-2021, 01:14 AM
Post: #5
RE: HP-21 repair
(10-15-2021 10:56 PM)teenix Wrote:  Other than that, as Bob pointed out, maybe the Arduous Calculator Thingy has failed.

Best expansion of ACT I've seen to date, thanks Tony!

(10-16-2021 12:46 AM)Benoit Maag Wrote:  Bob, Tony,
I will check with Bernhard and make it a 34C.

That's the spirit! When you get a lemon, make lemonade, or in this case, a super lemon drink with more taste, ice, and sweetness than any other similar drink.

--Bob Prosperi
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11-16-2021, 08:12 AM
Post: #6
RE: HP-21 repair
Worked like a charm !

   
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11-16-2021, 01:55 PM
Post: #7
RE: HP-21 repair
Super nice!! The comfort of a Woodstock with the power of a 34C.

Very good outcome, thanks for sharing the happy ending.

--Bob Prosperi
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